Control of gas fired appliances

ABSTRACT

Control means for a gas burner having a manually operable valve settable by a user to an off position or a maximum flow position or an intermediate position wherein there is provided a by-pass valve having a closure member movable between a closed position in which there is no flow of gas through the by-pass valve and an open position which provides for a greater rate of gas flow to the associated burner than the rate of flow which would be achieved by the manually operable valve alone when in an intermediate position, there being also provided a temperaturesensitive device which is arranged to effect movement of said bypass valve closure member from its open position to its closed position when the temperature sensed by said device attains a pre-determined value, and manually operable means for initially setting said closure member in its open position.

United States Patent Harding et al.

[ CONTROL OF GAS FIRED APPLIANCES [75] Inventors: Brian Harding, West Bromwich;

Arthur John Aldis, Solihull; Kenneth Edmund Collins, Sutton Coldfield, all of England [73] Assignee: Parkinson Cowan Appliances Limited, Birmingham, England [22] Filed: June 7, 1974 [21] Appl. No.: 477,407

[30] Foreign Application Priority Data June 13, 1973 United Kingdom 28063/73 [52] U.S. Cl. 236/1 A; 236/75 [51] Int. Cl. F24B 3/12 [58] Field of Search 236/1 A, 15 A, 75

[56] References Cited UNITED STATES PATENTS 1,881,637 10/1932 Johnson 236/15 A 2,383,641 8/1945 Focke et al. 236/75 Primary ExaminerWilliam E. Wayner Attorney, Agent, or Firm-Holman & Stern ABSTRACT Control means for a gas burner having a manually operable valve settable by a user to an off position or a maximum flow position or an intermediate position wherein there is provided a by-pass valve having a closure member movable between a closed position in which there is no flow of gas through the by-pass valve and an open position which provides for a greater rate of gas flow to the associated burner than the rate of flow which would be achieved by the manually operable valve alone when in an intermediate position, there being also provided a temperature-sensitive device which is arranged to effect movement of said bypass valve closure member from its open position to its closed position when the temperature sensed by said device attains a pre-determined value, and manually operable means for initially setting said closure member in its open position.

4 Claims, 5 Drawing Figures U.S. Patent Oct. 14, 1975 Shfiet 1 012 3,912,161

\ FIGZ.

US. Patent Oct. 14, 1975 Sheet 2 of2 3,912,161

FIG.4.

FIGE.

CONTROL OF GAS FIRED APPLIANCES This invention relates to the control of gas-fired appliances and especially (but not exclusively) to the control of burners (such as a hotplate burner) of a domestic cooker. One object of the invention is to provide improved gas burner vcontrol means which, inter alia, can be used so that the associated gas burner will automatically provide a maximum heat output for an initial period, followed by a reduced heat output.

In accordance with the invention, there is provided gas burner control means comprising a manually operable valve which can be set by a user to an off position or a maximum flow position or an intermediate position in which in use the rate of flow of gas through the valve will be less than the maximum rate of flow, a by-pass valve (33, 31, 30) having a closure member (32) which is movable between open and closed positions, said bypass valve being arranged in use to provide, when said closure member is in its open position and when said manually operable valve is in an intermediate position, a rate of gas flow to the associated burner which is greater than the rate of gas flow which would be achieved by said manually operable valve alone in said intermediate position, a temperature-sensitive device (THl) which is arranged automatically to control the operation of said by-pass valve so as to effect movement of said closure member from its open position to its closed position when the temperature sensed by said temperature-sensitive device attains a pre-determined value, and manually operable means (PBl) for initially setting said closure member in its open position.

Control means as above-defined can be used, for example, to control the operation of a gas-fired hot plate on which it is required to heat a liquid in a container relatively quickly to boiling point, whereafter it is required to reduce the heat output of the hot plate so as to keep the liquid in the container simmering at a predetermined rate. To this end, said manually operable valve would be set to an intermediate position which, from experience and without the assistance of gas flow from the by-pass valve, would give the required simmering condition after the liquid has boiled. Said manually-operable means would then be operated to set said by-pass valve closure member in its open position whereupon gas flow to the burner, augmented by flow through the by-pass valve, would result in a rapid heating up of the liquid to a pre-determined temperature (e.g. slightly below the boiling point) when the aforesaid temperature-sensitive device sensing the temperature of the bottom of said container, would act to close said by-pass valve and reduce the rate of gas flow to the burner to that provided by the manuallyoperable valve in its intermediate position. On the other hand, if said manually operable means is not initially operated to open said by-pass valve closure memher, then the burner would be entirely under the control of said manually operable valve.

The invention will now be more particularly described with reference to the accompanying drawings wherein FIGS. 1, 2, 3 and 4 are schematic sectional views showing parts of one example of control means in accordance with the invention, said drawings showing, inter alia, a by-pass valve and a manually operable valve (which is seen in different alternative positions in FIGS. 1 to 4) for controlling the rate of flow of gas to a burner such as a hotplate burner of a domestic cooker, and

FIG. 5 is a circuit diagram which illustrates one way in which a temperature sensitive device can be used to control the operation of the by-pass valve.

Throughout the views of FIGS. 1 thru 3, the gas flow to the burner is indicated by the arrows. The full arrows indicate gas flow through the main or manually operable valve, whereas the dotted arrows indicate the flow path through the by-pass valve when the latter is open, it being understood, of course, that in FIGS. 2 and 3, the by-pass valve is shown in the closed position. If, however, such by-pass valve were open, then the gas flow would be as indicated by the dotted arrows.

Referring firstly to FIGS. 1 to 4 the right hand side of each Figure shows a manually operable valve which comprises a manually rotatable plug 10 having a transverse drilling 18 and an axial passage 19, the latter being connected in use to the gas burner it is desired to control. Said plug 10 is set in a housing 11 having a pas sage 13 which is arranged to receive gas from a main supply pipe 34. In FIG. 1 the manually rotatable plug 10 is seen in a full on or maximum flow condition in which gas flowing from said main supply pipe 34 will flow through the passage 13 and thence through the passages 18 and 19 to the burner. The burner will then be operated at maximum heat output.

The plug 10 can however also be set in an intermediate position designed to permit a reduced flow of gas to pass through the plug to the burner and in the example now described means for producing such a reduced flow may be provided as described in our Co-pending Application No. 59508/71 in which gas flowing from the passage 13 can enter a recess 20 in the plug 10 from whence it is transferred to a further recess 21 formed in said plug and thence via one or more passages 16 through a channel (not shown) formed in a face of an elastomeric pad 22 mounted on the housing 11.

FIG. 2 illustrates one such intermediate or reduced flow position of the plug 10, the latter having been turned clockwise from the maximum flow condition seen in FIG. 1. FIG. 3 shows another intermediate position in which the plug 10 has been turned through a further small angle in a clockwise direction and continued clockwise rotation of said plug 10 will result in the off position seen in FIG. 4 being reached in which gas from the passage 13 cannot enter the passage 18 or the recess 20. FIGS. 2 and 3 represent approximately the two limits of the intermediate positions of the plug 10 between a full on position and an off position. It is however to be understood that other forms of construction may be adopted if desired to produce intermediate or reduced flow rates between the full on and off positions.

FIGS. 1 to 4 also show in the left hand side of the housing 11 a by-pass valve comprising passages 33, 31 and 30, said valve also having a ball shaped closure member 32. The passage 33 is also arranged to receive gas from the main supply pipe 34 but clearly when the closure member 32 is in its lower position as shown in full lines in FIGS. 1 to 4 the by-pass valve will be closed and no gas can pass from passage 31 to passage 30. Said closure member 32 is however controlled by a solenoid 36 having an armature 35 so that the solenoid 36 can be energised as will be hereinafter described to lift said closure member 32 and permit gas to flow through the by-pass valve into passage 30.

Referring now to FIGS. 2 and 3 which, as previously mentioned, show the manually operable valve 10 in two intermediate positions it will be appreciated that passage 30 is in communication with the passage 18 in said plug 10. If therefore in either said intermediate positions the closure member 32 is in its open or upper position gas would be able to flow through the by-pass valve into passage 30 and then into the passage 18 of the plug 10 to augment the flow of gas through the plug 10 to the associated burner. With the plug 10 in its full on or off positions as shown in FIGS. 1 and 4 respectively however no gas can pass from the by-pass valve to the burner even if the closure member 32 is in an open position since the plug 10 will not be in a position to accept a flow of gas from passage 30.

Control means in accordance with the present invention also includes a temperature-sensitive device and in the example now described this device comprises a thermistor which may for example have a resistance of 47,000 ohms at 25C and about 3,500 ohms at 90C. In use said temperature-sensitive element would be arranged so that it senses the temperature of the bottom ofa container which in use would be placed on the hotplate which is heated by the burner.

Reference is now made to FIG. 5 which is a circuit diagram illustrating the way in which the aforesaid thermistor can be used to control the operation of said closure member 32 of the by-pass valve. As shown in FIG. 5 there is a transformer TF1 with centre tapped secondary which provides full wave rectification through diodes D1 and D2 so that the wave form at A is as sketched, falling to zero at each half-cycle. A further diode D3, resistance R9 and capacitor C1 produces smoothed direct current at B.

The solenoid coil S1 (corresponding to 36 in FIGS. l-4), shunted by a diode D4, is placed in series with a controlling resistance R10 and the anode-cathode terminals of the thyristor TYl across the unsmoothed supply at A.

A potentiometer consisting of resistances R7, R8 and diode D6 provides sufficient voltage at the thyristor gate to trigger it provided that no current flows through the diode D5.

Temperature is sensed by a bridge circuit in which the resistance R1 and R2 is balanced against the resistance of the aforesaid thermistor indicated by THl. The ratio arms on the other side of the bridge are R3 and R4, and R5. The tripping point of the circuit is reached when the resistance of the thermistor has fallen to a value which makes the potential of Q the same as the potential of P. At lower thermistor temperature (higher resistance) the potential of Q is higher than that of P and no current can flow through transistors TR1 and TR2 since both have reverse biassed junctions.

As soon as the potential of Q falls below that of P emitter-base current flows in TR1 causes it to conduct. This passes base-emitter current through TR2 and causes it to conduct. When TR2 conducts resistance R6 is effectively in parallel with THl. The value of R6 is chosen so that, while TR2 conducts, the potential of Q can never rise above that of P and the circuit will remain tripped (i.e. both TR1 and TR2 conduct) whatever the resistance of TI-Il may become.

If the resistance of THl is above the trip" value the circuit may be re-set by pressing and releasing a pushbutton PBl. This action breaks the current through R6 and allows the potentials of P & Q to assume their bridge values.

A zener diode ZDI prevents the voltage across the transistor circuit from exceeding a safe voltage: typically 15 volts.

The circuit can be tripped at will at any time by briefly closing the switch SW1 (which mechanically is connected to the plug 10) and opening it again. This short circuits part of the top ratio arm of the bridge, values being chosen so that the potential of P rises above the zener voltage of ZDl, a condition which will always trip the circuit. Once tripped, the current through R6 will hold it in that condition.

When the circuit is tripped, and the transistor TR2 conducts, the cathode of diode D5 is effectively earthed and the current diverted from the gate of thyristor TYl, thus switching it off when the voltage reaches zero in the next half cycle.

Diode D6 is used to offset the turn-on voltage of D5 which might otherwise be sufficient to keep the thyristor switched on. 1

When the circuit is first switched on, the capacitor C2 takes a short while to charge through resistance R1 and R2 and during this time the potential of Q- is below that of P. This ensures that the circuit will always be switched on into the tripped condition. C2 also absorbs any AC pick up in the termistor leads which might cause spurious tripping.

Thus when the circuit is tripped the solenoid coil 36 (see FIGS. 1 to 4) will not be energised and the closure member 32 will be in its lower position closing the bypass valve. The circuit will always trip if the switch SW1 is closed i.e. if the plug 10 is set in the off position or if the temperature of the thermistor rises above the predetermined value which may for example be slightly below the boiling point of the liquid which is being heated on the hotplate. The variable resistance R2 can be used to adjust this predetermined value. Furthermore, once the circuit is tripped it will remain in a tripped condition until it is reset by operating the push button PBl, pressing of said button serving to re-set the circuit, energise the solenoid 36 and raise the closure member 32 to open the by-pass valve. The potentiometer R7 and D6 and R8 and the diode D5 are used to prevent the bridge circuit from being affected by the thyristor gate current when the circuit is not tripped.

Thus in operation when it is desired to use the above described control means the plug 10 will be turned from its off position, the circuit remaining tripped by reason of previous operation of the switch SW1 as the plug 10 was last closed. The plug 10 can then be turned to an intermediate position which will give, from experience, the required simmering rate of gas flow and the push button P81 is next pressed so as to re-set the circuit, energise the solenoid 36 and open the by-pass valve. This enables an augmented flow of gas to flow through the plug 10 to the burner so that the liquid in a container placed on the hotplate will be heated relatively rapidly. When such liquid reaches the desired temperature as sensed by the aforesaid thermistor which senses the temperature of the bottom of the container the circuit will be tripped and the solenoid will be tie-energised so that the closure member 32 resumes its closed position to shut off the by-pass valve and reduce the flow of gas to the burner to the simmering rate previously selected. If desired the gas burner can now be controlled entirely manually. Furthermore the burner can in any event be controlled manually if, in the first instance, the push button PB] is not operated.

ln alternative embodiments instead of using a thermistor as above described other forms of temperature sensitive elements can be used and furthermore such elements can be arranged to control the operation of the by-pass valve in any convenient way such as for example by mechanical means or electro mechanical means.

We claim:

1. Gas burner control means comprising a manually operable valve which can be set by a user to an off position or a maximum flow position or an intermediate position in which in use the rate of flow of gas through the valve will be less than the maximum rate of flow, a bypass valve having a closure member which is movable between open and closed positions, said by-pass valve being arranged in use to provide, when said closure member is in its open position and when said manually operable valve is in an intermediate position a rate of gas flow to the associated burner which is greater than the rate of gas flow which would be achieved by said manually operable valve alone in said intermediate position, a temperature-sensitive device which is arranged automatically to control the operation of said by-pass valve so as to effect movement of said closure member from its open position to its closed position when the temperature sensed by said temperature-sensitive device attains a pre-determined value, and manually operable means for initially setting said closure member in its open position.

2. Gas burner control means as claimed in claim 1 wherein said closure member of the by-pass valve is movable to its open position by means of a solenoid which is actuable by said temperature-sensitive device.

3. Gas burner control means as claimed in claim 2 wherein there are provided means operatively connected to said manually operable valve for setting said closure member of the by-pass valve into its closed position as said manually operable valve is moved manually into its off position from an intermediate position.

4. Gas burner control means as claimed in claim 3 wherein said temperature-sensitive device comprises a thermistor conneted in an electrical circuit which includes said solenoid and which also includes a switch forming said means operatively connected to said manually operable valve, said manually operable means for initially setting said closure member in its open position comprising a further switch which is also connected in said circuit. 

1. Gas burner control means comprising a manually operable valve which can be set by a user to an off position or a maximum flow posiTion or an intermediate position in which in use the rate of flow of gas through the valve will be less than the maximum rate of flow, a by-pass valve having a closure member which is movable between open and closed positions, said by-pass valve being arranged in use to provide, when said closure member is in its open position and when said manually operable valve is in an intermediate position, a rate of gas flow to the associated burner which is greater than the rate of gas flow which would be achieved by said manually operable valve alone in said intermediate position, a temperature-sensitive device which is arranged automatically to control the operation of said by-pass valve so as to effect movement of said closure member from its open position to its closed position when the temperature sensed by said temperature-sensitive device attains a pre-determined value, and manually operable means for initially setting said closure member in its open position.
 2. Gas burner control means as claimed in claim 1 wherein said closure member of the by-pass valve is movable to its open position by means of a solenoid which is actuable by said temperature-sensitive device.
 3. Gas burner control means as claimed in claim 2 wherein there are provided means operatively connected to said manually operable valve for setting said closure member of the by-pass valve into its closed position as said manually operable valve is moved manually into its off position from an intermediate position.
 4. Gas burner control means as claimed in claim 3 wherein said temperature-sensitive device comprises a thermistor conneted in an electrical circuit which includes said solenoid and which also includes a switch forming said means operatively connected to said manually operable valve, said manually operable means for initially setting said closure member in its open position comprising a further switch which is also connected in said circuit. 